screenless displays seminar report
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Dept. of ECE SDMIT, UJIRE Page 1
Screenless display is the present evolving technology in the field of the computer-
enhanced technologies. It is going to be the one of the greatest technological development
in the coming future years.
Several patents are still working on this new emerging technology which can
change the whole spectacular view of the screenless displays. Screen less display
technology has the main aim of displaying (or) transmitting the information without any
help of the screen (or) the projector. Screen less displays have become a new rage of
development for the next GEN-X. Screenless videos describe systems fortransmitting
visual information from a video source without the use of the screen.
Screen less computing systems can be divided mainly into 3 groups:
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2.1 VISUAL IMAGE
Visual Image screen less display includes any screen less image that the eye can
perceive as shown in figure 1 and 2. The most common example of Visual Image screen
less display is a hologram.
2.1.1 HOLOGRAM Holograms were used mostly in telecommunications as an alternative to screens.
Holograms could be transmitted directly, or they could be stored in various storage
devices (such as holodiscs) the storage device can be hooked up with a holoprojector in
order for the stored image to be accessed . Debatably, virtual reality goggles (which
consist of two small screens but are nonetheless sufficiently different from traditional
computer screens to be considered screen less) and heads-up display in jet fighters (which
display images on the clear cockpit window) also are included in Visual Image category.
In all of these cases, light is reflected off some intermediate object (hologram, LCD
panel, or cockpit window) before it reaches the retina. In the case of LCD panels the light
is refracted from the back of the panel, but is nonetheless a reflected source. The new
software and hardware will enable the user to, in effect; make design adjustments in the
system to fit his or her particular needs, capabilities, and preferences. They will enable
the system to do such things as adjusting tousers behaviors in dealing with interactive
Working of hologram To create a hologram, you need an object (or person) that you want to record; a
laser beam to be shined upon the object and the recording medium; a recording medium
with the proper materials needed to help clarify the image; and a clear environment to
enable the light beams to intersect.
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Fig.2.1 Recording a hologram.
A laser beam is split into two identical beams and redirected by the use of mirrors.
One of the split beams, the illumination beam or object beam, is directed at the object.
Some of the light is reflected off the object onto the recording medium.
The second beam, known as the reference beam, is directed onto the recording
medium. This way, it doesn't conflict with any imagery that comes from the object beam,
and coordinates with it to create a more precise image in the hologram location.
The two beams intersect and interfere with each other. The interference pattern is
what is imprinted on the recording medium to recreate a virtual image for our eyes to see.
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Fig.2.2 Reconstructing a hologram
The diffraction grating and reflective surfaces inside the hologram recreate the
original object beam. This beam is absolutely identical to the original object beam
before it was combined with the reference wave. This is what happens when you listen to
the radio. Your radio receiver removes the sine wave that carried the amplitude- or
frequency-modulated information. The wave of information returns to its original state,
before it was combined with the sine wave for transmission.
The beam also travels in the same direction as the original object beam, spreading out as
it goes. Since the object was on the other side of the holographic plate, the beam travels
toward you. Your eyes focus this light, and your brain interprets it as a three-dimensional
image located behind the transparent hologram. This may sound far-fetched, but you
encounter this phenomenon every day. Every time you look in a mirror, you see yourself
and the surroundings behind you as though they were on the other side of the mirror's
surface. But the light rays that make this image aren't on the other side of the mirror --
they're the ones that bounce off of the mirror's surface and reach your eyes. Most
holograms also act like color filters, so you see the object as the same color as the laser
used in its creation rather than its natural color.
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This virtual image comes from the light that hits the interference fringes and
spreads out on the way to your eyes. However, light that hits the reverse side of each
fringe does the opposite. Instead of moving upward and diverging, it moves downward
and converges. It turns into a focused reproduction of the object -- a real image that you
can see if you put a screen in its path. The real image is pseudoscopic, or flipped back to
front -- it's the opposite of the virtual image that you can see without the aid of a screen.
With the right illumination, holograms can display both images at the same time.
Your brain plays a big role in your perception of both of these images. When your
eyes detect the light from the virtual image, your brain interprets it as a beam of light
reflected from a real object. Your brain uses multiple cues, including, shadows, the
relative positions of different objects, distances and parallax, or differences in angles, to
interpret this scene correctly. It uses these same cues to interpret the pseudoscopic real
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2.2 RETINAL DISPLAY
Virtual retinal display systems are a class of screen less displays in which images
are projected directly onto the retina as shown in figure 2.2. They are distinguished from
visual image systems because light is not reflected from some intermediate object onto
the retina; it is instead projected directly onto theretina. Retinal Direct systems, once
marketed, hold out the promise of extreme privacy when computing work is done in
public places because most inquiring relies on viewing the same light as the person who
is legitimately viewing the screen, and retinal direct systems send light only into the
pupils of their intended viewer.
Fig 2.3 Block Diagram of Retinal Display
To create an image with the VRD a photon source (or three sources in the case of
a color display) is used to generate a coherent beam of light. The use of a coherent source
(such as a laser diode) allows the system to draw a diffraction limited spot on the retina.
The light beam is intensity modulated to match the intensity of the image being rendered.
The modulation can be accomplished after the beam is generated. If the source has
enough modulation bandwidth, as in the case of a laser diode, the source can be
The resulting modulated beam is then scanned to place each image point, or pixel,
at the proper position on the retina. A variety of scan patterns are possible. The scanner
could be used in a calligraphic mode, in which the lines that form the image are drawn
directly, or in a raster mode, much like standard computer monitors or television. Our
development focuses on the raster method of image scanning and allows the VRD to be
driven by standard video sources. To draw the raster, a horizontal scanner moves the
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beam to draw a row of pixels. The vertical scanner then moves the beam to the next line
where another row of pixels is drawn.
After scanning, the optical beam must be properly projected into the eye. The goal
is for the exit pupil of the VRD to be coplanar with the entrance pupil of the eye. The lens
and cornea of the eye will then focus the beam on the retina, forming a spot. The position
on the retina where the eye focuses the spot is determined by the angle at which light
enters the eye. This angle is determined by the scanners and is continually varying in a
raster pattern. The brightness of the focused spot is determined by the intensity
modulation of the light beam. The intensity modulated moving spot, focused through the
eye, draws an image on the retina. The eye's persistence allows the image to appear
continuous and stable.
Finally, the drive electronics synchronize the scanners and intensity modulator
with the incoming video signal in such a manner that a stable image is formed.
Fig.2.4 Retinal Display
2.2.1 VRD STRUCTURE
A virtual retinal display (VRD), also known as a retinal scan display (RSD), is a
new display technology that draws a raster